1. Field of the Invention
The present invention relates to the preparation of subterranean formation treatment fluids, and more particularly, but not by way of limitation, apparatus and methods for preparing viscous treatment gels with dry polymer and water.
2. Description of the Related Art
In the oil drilling and production industry, viscous aqueous fluids are commonly used in treating subterranean wells, and as carrier fluids. Such fluids may be used as fracturing fluids, acidizing fluids, and high-density completion fluids. In an operation known as well fracturing, such fluids are used to initiate and propagate underground fractures for increasing oilwell productivity.
Viscous fluids, such as gels, are typically an aqueous solution of a polymer material. A common continuous method used to prepare viscous fluids at an oilwell site, involves the use of initial slurry of the polymer material in a hydrocarbon carrier fluid (i.e. diesel fluid) which facilitates the polymer dispersion and slurry mixing. Although this process achieves the required gel quality, the presence of hydrocarbon fluids is often objected to in particular fields, even though the hydrocarbon represents a relatively small amount of the total fracturing gel once mixed with water. Also, there are environmental problems associated with the clean-up and disposal of both hydrocarbon-based concentrates and well treatment gels containing hydrocarbons; as well as with the clean-up of the tanks, piping, and other handling equipment which have been contaminated by the hydrocarbon-based gel.
Other applications used for the continuous mixing of viscous treatment gels include gelling the polymer in a hydrocarbon carrier that is mixed with water to produce the fracturing gel which is then flowed through baffled tanks providing first-in/first-out (FIFO) flow pattern, and allowing for the hydration time of the gel. Yet, another technique for mixing of dry polymer directly to produce viscous treatment gels is described in Allen, U.S. Pat. No. 5,426,137, Allen, U.S. Pat. No. 5,382,411, and Harms et al., U.S. Pat. No. 5,190,374. These techniques, while potentially effective, require several complicated steps to prepare the gel, which presents drawbacks in an oilwell setting. Further, U.S. Patent Application 2004/0256106 A1 discloses an apparatus without an eductor, for substantially hydrating a gel particulate using a mixer in conjunction with an impeller located within the mixer housing, which prevents formation of gel balls.
Therefore, there is a need for apparatus and methods useful for hydrating a dry polymer constituents directly for preparing viscous treatment gels in a continuous mode without the use of the hydrocarbon carrier fluid, and such need is met, at least in part, by the following invention.